Fresnel lens angular segment manufacturing apparatus and method

ABSTRACT

A roller extruder for manufacturing Fresnel lens angular segments from raw sheet plastic, the roller extruder having a blank roller and a die roller positioned a desired roller clearance from the blank roller, the die roller having two peripheral lens dies with an angular displacement between the lens dies increasing linearly from a die junction at the inside roller edge to approximately one hundred eighty degrees at the outside roller edge, and the die roller having peripheral Fresnel facet dies.

BACKGROUND OF THE INVENTION

This invention is in the field of apparatuses and methods formanufacturing Fresnel lenses and in particular apparatuses and methodsfor extruding Fresnel lens angular segments from plastic.

Processes for extruding sheet plastic from raw plastic material such asingots and pellets and the like are well known in the industry.Similarly, processes for extruding Fresnel lenses from plastic throughthe use of heat and roller equipment for the extrusion process and diesfor impressing the facet grooves on the face of the lens are known inthe industry.

The use of Fresnel lenses for solar collectors is also known in theindustry. Economic, operational, and maintenance considerations dictatethat the use of a larger collector for solar collection applications isdesirable. When a Fresnel lens is to be used for a solar collector, thisusually dictates that the solar collector cannot be constructed of asingle lens. Also, in the manufacturing of the Fresnel lens, ordinarilya size limitation is dictated by the size of the rollers that are usedfor the production of the Fresnel lens. This then requires that a solarcollector be constructed from a composite of Fresnel lens components. Itis also found that the use of a generally circular shape for a Fresnellens is desirable for solar collector applications. Because of facetgroove orientation limitations and geometric sizing and shapelimitations, the manufacturing of Fresnel lens components for agenerally circular solar collector is problematic.

An object of the present invention is to provide an apparatus and amethod for manufacturing Fresnel lens components for a generallycircular solar collector that will provide for the matching of Fresnellens facet grooves of the components with the desired overall pattern ofthe solar collector and will provide for economy in manufacturing,including the use of common size rollers and other common extrusionequipment and the minimization of material waste. For purposes of thisapplication, the term “generally circular” shall be defined to includepolygon shapes such as an octagonal or hexagonal shape which have sideswhich are roughly equidistant from the geometric center of thecollector.

SUMMARY OF THE INVENTION

A preferred apparatus and method of the present invention utilizes a tworoller extruder that is equipped with a blank roller and a die roller.The die roller is equipped with one or more peripheral lens dies. Thelens dies provide, as the blank roller and the die roller rotate throughone complete revolution, for the extrusion of a pair of lenssubsegments, comprising a first or inner lens subsegment and a second orouter lens subsegment.

The die roller also has Fresnel facet dies for impressing Fresnel facetgrooves in the first lens subsegment and the second lens subsegment in apattern that provides for the Fresnel facet grooves to have a commoncenter of curvature when the first lens subsegments and the second lenssubsegments are positioned in a solar collector. The Fresnel facet diesalso provide for an appropriate progression of the Fresnel grooving withdistance from the common center of curvature so that solar energyincident to and passing the solar collector will be focused roughly to acommon focal point or common focal field.

A power shaft or other means known to persons skilled in the art can beused to provide power to the blank roller shaft and the die rollershaft, with the blank roller and the die roller having a power link andpreferably being driven at the same speed from the same power source.

A raw plastic sheet is fed to the rollers and successive pairs of thefirst lens subsegment and the second lens subsegment are discharged. Theraw plastic sheet can be supplied from a roll of blank plastic sheetingor can be supplied from a raw sheet extruder using raw plastic pellets,ingots or the like. Depending upon the plastic being used, the desiredthickness of the angular lens segments and other factors, thetemperature of the raw plastic sheet will likely need to be controlled.The inventor of the present invention prefers to deploy the method ofthe present invention downstream of a raw sheet extruder which willnormally discharge the raw sheet plastic in a pliable condition at anelevated temperature.

A continuous stream of successive pairs of angular lens segmentcomponents, namely a first lens subsegment and a second lens subsegment,each pair being fitted together to form an angular lens segment for asolar collector can be produced using the method of the presentinvention. The method of the present invention also provides foreliminating or minimizing the waste of raw plastic material.

Generally longitudinal lens dies on the die roller impress the left edgeand the right edge of each successive first lens subsegment and the leftedge and the right edge of each successive second lens subsegment, thefirst right edge of each first lens subsegment being impressed proximalto the second right edge of an adjacent second lens subsegment, and thefirst left edge of each first lens subsegment being impressed proximalto the second left edge of an adjacent second lens subsegment. Optionalend lens dies at the opposing die roller ends may also be used toimpress the inner edges and the outer edges of each successive firstlens subsegment and each successive second lens subsegment. Fresnelfacet dies on the die roller impress Fresnel facet grooves on eachsuccessive first lens subsegment and each successive second lenssubsegment. The Fresnel facet die pattern impresses a Fresnel facetgroove pattern with facet grooves for each angular lens segment having acommon center of curvature and progressive refraction, thus providingfor focus of incident solar radiation on a common focal point or commonfocal zone.

Depending upon the diameter of the die roller and the desired dimensionsof the angular lens segments, the orientation of the lens die may bechanged to be oriented generally circumferential rather than generallylongitudinal on the die roller, re-orienting the general layout of thefirst lens subsegment and the second lens subsegment on the die rollerby ninety degrees. For that embodiment, the first inner edge and thesecond outer edge is impressed by a longitudinal lens dye and isproximal to the first outer edge and the second inner edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of a preferred embodiment of a rollerextruder of the present invention utilized for a preferred embodiment ofthe method of the present invention to manufacture Fresnel lens angularsegments.

FIG. 2 is a vertical side view cross-section of the roller extruder ofFIG. 1 utilized to manufacture Fresnel lens angular segments.

FIG. 3 is a plan view detail of two successive pairs of Fresnel lenssubsegments manufactured through use of a preferred embodiment of theroller extruder of FIG. 1 and a preferred embodiment of the method ofthe present intention.

FIG. 4 is a plan view of a hexagon shaped solar collector utilizingFresnel lens angular segments comprised of Fresnel lens subsegmentsmanufactured through use of the preferred embodiment of the rollerextruder of FIG. 1 and a preferred embodiment of the method of thepresent invention.

FIG. 5 is a front elevation view of an alternative preferred embodimentof a roller extruder of the present invention utilized for a alternativepreferred embodiment of the method of the present invention tomanufacture Fresnel lens angular segments.

FIG. 6 is a vertical side view cross-section of the alternative rollerextruder of FIG. 5 utilized to manufacture Fresnel lens angularsegments.

FIG. 7 is a plan view detail of two successive pairs of Fresnel lenssubsegments manufactured through use of an alternative preferredembodiment of the roller extruder of FIG. 5 and an alternative preferredembodiment of the method of the present intention.

FIG. 8 is a plan view of a hexagon shaped solar collector utilizingFresnel lens angular segments comprised of Fresnel lens subsegmentsmanufactured through use of the alternative preferred embodiment of theroller extruder of FIG. 5 and an alternative preferred embodiment of themethod of the present invention.

FIG. 9 is a cross-section detail of an alternative embodiment of aFresnel lens subsegment manufactured with matching Fresnel facet grooveson both the front subsegment surface and the rear subsegment surface.

FIG. 10 is a cross-section detail of an alternative embodiment of aFresnel lens subsegment manufactured with non-matching Fresnel facetgrooves on the front subsegment surface and the rear subsegment surface.

DETAILED DESCRIPTION

Referring first to FIG. 1, a preferred embodiment of the roller extruder1 of the present invention having a blank roller 3 and a die roller 5 isshown. The die roller, for the preferred embodiment shown is equippedwith two peripheral lens dies 7. Referring also to FIG. 2 and FIG. 3,the lens dies provide, as the blank roller and the die roller rotatethrough one complete revolution 9, for the extrusion of a lens wafer 105having a pair of lens subsegments 11, comprising a first or inner lenssubsegment 13 and a second or outer lens subsegment 15. The die rolleralso has Fresnel facet dies 75 for impressing, as the die roller isrotated through a complete rotation, Fresnel facet grooves 77 in thefirst lens subsegment and the second lens subsegment in a pattern thatprovide for the Fresnel facet grooves to have a common center ofcurvature 79 when the first lens subsegments and the second lenssubsegments are positioned in a solar collector 45 as shown in FIG. 4.The Fresnel facet dies also provide for an appropriate progression ofthe Fresnel grooving with distance from the common center of curvatureso that solar energy incident to and passing the solar collector will befocused roughly to a common focal point or common focal field.

Referring again to FIG. 1, the first lens die 113 and the second lensdie 115 are angularly separated by a primary angular displacement 111between the first lens die and the second lens die which increaseslinearly from the die junction 117, which is proximal to the firstroller inner edge 123, to the first die end 119 and the second die end121, which are proximal to the first roller outer edge 125. The firstlens die and the second lens die may be joined or proximally joined atthe die junction. The angular displacement between the first lens die atthe first die end and the second lens die at the second die end for thepreferred embodiment shown is approximately one hundred eighty degrees(180°). This is true whether the first lens die is generally horizontalas shown for the embodiment illustrated in FIG. 1 and FIG. 2 or thefirst lens die and the second lens die are both angularly displaced asshown for the alternative embodiment illustrated in FIG. 5 and FIG. 6.

Referring again to FIG. 1 and FIG. 2, a power shaft 83 can be used toprovide power to the blank roller shaft 55 and the die roller shaft 59,with the blank roller and the die roller having a power link 57 andpreferably being driven at the same speed from the same power source.Sprockets on the roller shaft and die roller shaft with chains or beltspositively linking the rollers provides for the roller speed of theblank roller and the die roller to be equal. Other roller drivemechanisms for driving the rollers will be known to persons skilled inthe art.

A pair of lower roller supports 63, 67 and a pair of upper rollersupports 61, 65 maintain a desired roller clearance 79 between the blankroller periphery 73 and the die roller periphery 71, which determinesthe Fresnel lens thickness 81 of the finished lens output 49 which willbe comprised of successive pairs of lens subsegments, a first lenssubsegment 13 and a second lens subsegment 15. Shaft bearings 107provide for the free rotation of the rollers on the support structure.The raw plastic sheet 47 is fed to the rollers upon a feed platform 51and successive pairs of the first lens subsegment and the second lenssubsegment as impressed in the lens wafer are discharged upon adischarge platform 53. Other roller support structures for supportingthe rollers and maintaining the desired roller clearance between theblank roller periphery and the die roller periphery will be known topersons skilled in the art.

The raw plastic sheet can be supplied from a roll of blank plasticsheeting or can be supplied from a raw sheet extruder using raw plasticpellets, ingots or the like. Depending upon the plastic being used, thedesired thickness of the angular lens segments and other factors, thetemperature of the raw plastic sheet will likely need to be controlled.The inventor of the present invention prefers to deploy the method ofthe present invention downstream of a raw sheet extruder which willnormally discharge the raw sheet plastic in a pliable condition at anelevated temperature. As noted above, the temperature of the raw sheetplastic that is optimum for the method of the present invention willdepend on the plastic being used, the thickness of the plastic and otherfactors that will be unique to each installation.

Referring again to FIG. 3, two successive pairs of angular lens segmentcomponents, namely a first lens subsegment 13 and a second lenssubsegment 15, each pair being fitted together to form an angular lenssegment 41 for a solar collector 45 as shown in FIG. 4 illustrate thecontinuous stream of angular lens segments that can be produced usingthe method of the present invention. The first lens subsegment has afirst inner edge 31 with a first inner generally circumferentialdimension 83, a first outer edge 27 with a first outer generallycircumferential dimension 85, a first left edge 37 with a first leftdimension 87 and a first right edge 39 with a first right dimension 89.The second lens subsegment has a second inner edge 25 with a secondinner generally circumferential dimension 91, a second outer edge 29with a second outer generally circumferential dimension 93, a secondleft edge 35 with a second left dimension 95, and a second right edge 33with a second right dimension 97, the first outer generallycircumferential dimension being roughly equal to the second innergenerally circumferential dimension providing for the second lenssubsegment to fit against the first lens subsegment with the secondinner edge fitting against the first outer edge for assembling anangular lens segment for a solar collector 45 as shown in FIG. 4, thefirst lens subsegment having a first radial dimension 99 from the firstinner edge to the first outer edge, the second lens subsegment having asecond radial dimension 101 from the second inner edge to the secondouter edge.

For the embodiment shown, the generally longitudinal lens dies 7 on thedie roller impress the left edge and the right edge of each successivefirst lens subsegment and the left edge and the right edge of eachsuccessive second lens subsegment, the first right edge of each firstlens subsegment being impressed proximal to the second right edge of anadjacent second lens subsegment, and the first left edge of each firstlens subsegment being impressed proximal to the second left edge of anadjacent second lens subsegment. Fresnel facet dies 75 on the die rollerimpress Fresnel facet grooves 77 on each successive first lenssubsegment and each successive second lens subsegment, the Fresnel facetdie pattern impresses a Fresnel facet groove pattern with facet groovesfor each angular lens segment having a common center of curvature andprogressive refraction, thus providing for focus of incident solarradiation on a common focal point or common focal zone.

Optional end lens dies 69 at the opposing die roller ends 103 may beused to impress the inner edges and the outer edges of each successivefirst lens subsegment and each successive second lens subsegment.However, the inventor prefers not to utilize end lens dies on the dieroller. This allows the inner edges and outer edges of the lens wafer toextend beyond the desired finish inner edges and outer edges of the lenssubsegments, thereby accommodating variations in the thickness of theraw plastic sheet, and allowing the lens subsegments to be trimmed,after extrusion, at the desired inner edges and desired outer edges.This reduces the probability of lens subsegments not fully extending tothe desired finish inner edge and the desired finish outer edge, whichrequires the rejection of the lens subsegments.

Depending upon the diameter of the die roller and the desired dimensionsof the angular lens segments, the orientation of the lens die whichimpresses the first left edge 37 and the second left edge 35 may bechanged to be oriented generally circumferential rather than generallylongitudinal on the die roller, re-orienting the general layout of thefirst lens subsegment and the second lens subsegment on the die rollerby ninety degrees. For that embodiment, the first inner edge 31 and thesecond outer edge 29 would be impressed by a longitudinal lens dye 7 andwould be proximal to the first outer edge 27 and the second inner edge25.

Referring now to FIG. 7, two successive pairs of Fresnel lenssubsegments manufactured through use of the alternative preferredembodiment of the roller extruder shown in FIG. 5 are shown. FIG. 8illustrates a plan view of a hexagonal shaped solar collector utilizingFresnel lens angular segments comprised of the Fresnel lens subsegmentsof FIG. 7 manufactured through use of the alternative preferredembodiment of the roller extruder of FIG. 5.

A further alternative embodiment of the two roller extruder of thepresent invention, that is used for an alternative embodiment of themethod of the present invention, consists of a first die roller and asecond die roller, the first die roller being substantially similar tothe die roller described above and shown in FIGS. 1-2 and FIGS. 5-6,having at least two generally longitudinal peripheral lens dies andperipheral first Fresnel facet dies. However, for this alternativeembodiment, the second die roller also has peripheral second Fresnelfacet dies. The second peripheral Fresnel facet dies of the second dieroller may match the first Fresnel facet dies, with the pattern of thematching second Fresnel facet dies being a mirror image of the patternof the first Fresnel facet dies, with the patterns of the Fresnel facetdies and the synchronization of the first die roller and the second dieroller providing for matching of first Fresnel facet grooves 127 on thefront subsegment surface 129 and second Fresnel facet grooves 131 on therear subsegment surface 133 of each lens subsegment 13,15 as shown inFIG. 9. Similarly the cross-sections and other dimensions of the firstFresnel facet dies and the second Fresnel facet dies may be generallythe same, providing for the cross-section 135 of first Fresnel facetgrooves and the cross-section 137 of the second Fresnel facet grooves tobe the same, as shown in FIG. 9. The effect of impressing matchingFresnel facet grooves on both surfaces of the lens subsegments is thatthe focal length of the lens is approximately one-half of the focallength of a comparable lens with Fresnel facet grooves impressed on onesurface only.

However, the spacing and dimensions of the second Fresnel facet dies donot necessarily have to be the same as the first Fresnel facet dies. Itis merely essential that the second Fresnel facet dies impress Fresnelfacet grooves on the rear subsegment surface of each successive firstlens subsegment and each successive second lens subsegment, which willprovide a grove pattern for each angular lens segment having a commoncenter of curvature, which center of curvature is directly opposite thecenter of curvature on the opposing front surface of the angular lenssegment, and will provide for progressive refraction, thus providing forfocus of incident solar radiation on a common focal point or commonfocal zone. First Fresnel facet grooves 127 and second Fresnel facetgrooves 131 having a differing cross-section are illustrated in FIG. 10.

Other embodiments and other variations and modifications of theembodiments described above will be obvious to a person skilled in theart. Therefore, the foregoing is intended to be merely illustrative ofthe invention and the invention is limited only by the following claimsand the doctrine of equivalents.

1. Roller extruder for manufacturing a Fresnel lens angular lenssegment, the roller extruder comprising: a) die roller having a firstroller inner edge and a first roller outer edge, having two peripherallens dies, a first lens die and a second lens die, which are proximallyjoined proximal to the first roller inner edge and have a primaryangular displacement of approximately one hundred eighty degreesproximal to the first roller outer edge, and having peripheral Fresnelfacet dies; b) blank roller; c) roller support structure; and d) rollerdrive mechanism.
 2. Roller extruder as recited in claim 1 wherein thedie roller has an axis of rotation and the first lens die is parallel tothe axis of rotation.
 3. Roller extruder as recited in claim 1 whereinthe die roller has an axis of rotation and the second lens die isparallel to the axis of rotation.
 4. Roller extruder as recited in claim1 further comprising a first end lens die extending circumferentiallyaround the die roller proximal to the first roller inner edge and asecond end lens die extending circumferentially around the die rollerproximal to the first roller outer edge.
 5. Roller extruder formanufacturing a Fresnel lens angular lens segment, the roller extrudercomprising: a) die roller having a first roller inner edge and a firstroller outer edge, having two peripheral lens dies, a first lens diehaving a first die end and a second lens die having a second die end,and having peripheral Fresnel facet dies, the first lens die and thesecond lens die being proximally joined at a die junction which isproximal to the first roller inner edge, and the first lens die and thesecond lens die being angularly separated by a primary angulardisplacement which increases approximately linearly with longitudinaldistance from the die junction to the first die end and the second dieend, the first die end and the second die end being proximal to thefirst roller outer edge, and the primary angular displacement betweenthe first die end and the second die end being approximately one hundredeighty degrees; b) blank roller; c) roller support structure; and d)roller drive mechanism.
 6. Roller extruder as recited in claim 5 whereinthe die roller has an axis of rotation and the first lens die isparallel to the axis of rotation.
 7. Roller extruder as recited in claim5 wherein the die roller has an axis of rotation and the second lens dieis parallel to the axis of rotation.
 8. Roller extruder as recited inclaim 5 further comprising a first end lens die extendingcircumferentially around the die roller proximal to the first rollerinner edge and a second end lens die extending circumferentially aroundthe die roller proximal to the first roller outer edge.
 9. Rollerextruder for manufacturing a Fresnel lens angular lens segment, theroller extruder comprising: a) first die roller having a first rollerinner edge and a first roller outer edge, having two peripheral lensdies which are proximally joined proximal to the first roller inner edgeand have a primary angular displacement of approximately one hundredeighty degrees proximal to the first roller outer edge, and havingperipheral first Fresnel facet dies; b) second die roller havingperipheral second Fresnel facet dies; c) roller support structure; andd) roller drive mechanism.
 10. Roller extruder as recited in claim 9wherein the first die roller has an axis of rotation and the first lensdie is parallel to the axis of rotation.
 11. Roller extruder as recitedin claim 9 wherein the first die roller has an axis of rotation and thesecond lens die is parallel to the axis of rotation.
 12. Roller extruderas recited in claim 9 wherein the first Fresnel facet dies have a firstcenter of curvature and the second Fresnel facet dies have a secondcenter of curvature and the second Fresnel facet dies are positioned onthe second die roller to provide for matching of the center of curvatureof the second Fresnel facet dies with the center of curvature of thefirst Fresnel facet by synchronization of first die roller rotation withsecond die roller rotation provided by the roller drive mechanism. 13.Roller extruder as recited in claim 9 further comprising a first endlens die extending circumferentially around the first die rollerproximal to the first roller inner edge and a second end lens dieextending circumferentially around the first die roller proximal to thefirst roller outer edge.
 14. Roller extruder for manufacturing a Fresnellens angular lens segment, the roller extruder comprising: a) first dieroller having a first roller inner edge and a first roller outer edge,having two peripheral lens dies, a first lens die having a first die endand a second lens die having a second die end, and having peripheralfirst Fresnel facet dies, the first lens die and the second lens diebeing proximally joined at a die junction which is proximal to the firstroller inner edge, and the first lens die and the second lens die beingangularly separated by a primary angular displacement which increasesapproximately linearly with longitudinal distance from the die junctionto the first die end and the second die end, the first die end and thesecond die end being proximal to the first roller outer edge, and theprimary angular displacement between the first die end and the seconddie end being approximately one hundred eighty degrees; b) second dieroller having peripheral second Fresnel facet dies; c) roller supportstructure; and d) roller drive mechanism.
 15. Roller extruder as recitedin claim 14 wherein the first die roller has an axis of rotation and thefirst lens die is parallel to the axis of rotation.
 16. Roller extruderas recited in claim 14 wherein the first die roller has an axis ofrotation and the second lens die is parallel to the axis of rotation.17. Roller extruder as recited in claim 14 wherein the first Fresnelfacet dies have a first center of curvature and the second Fresnel facetdies have a second center of curvature and the second Fresnel facet diesare positioned on the second die roller to provide for matching of thecenter of curvature of the second Fresnel facet dies with the center ofcurvature of the first Fresnel facet by synchronization of first dieroller rotation with second die roller rotation provided by the rollerdrive mechanism.
 18. Roller extruder as recited in claim 14 furthercomprising a first end lens die extending circumferentially around thefirst die roller proximal to the first roller inner edge and a secondend lens die extending circumferentially around the first die rollerproximal to the first roller outer edge.
 19. Roller extruder formanufacturing a Fresnel lens angular lens segment, the roller extrudercomprising: a) die roller having a first roller inner edge and a firstroller outer edge, having one or more pairs of peripheral lens dies,each pair comprising a first lens die and a second lens die which areproximally joined proximal to the first roller inner edge, each pairbeing spaced equidistant around the periphery of the die roller, andeach pair having a primary angular displacement approximately equal tothree hundred sixty degrees divided by the total number of lens dies,and having peripheral Fresnel facet dies; b) blank roller; c) rollersupport structure; and d) roller drive mechanism.
 20. Roller extruderfor manufacturing a Fresnel lens angular lens segment, the rollerextruder comprising: a) first die roller having a first roller inneredge and a first roller outer edge, having one or more pairs ofperipheral lens dies, each pair comprising a first lens die and a secondlens die which are proximally joined proximal to the first roller inneredge, each pair being spaced equidistant around the periphery of the dieroller, and each pair having a primary angular displacementapproximately equal to three hundred sixty degrees divided by the totalnumber of lens dies, and having peripheral first Fresnel facet dies; b)second die roller having peripheral second Fresnel facet dies; c) rollersupport structure; and d) roller drive mechanism.
 21. Method formanufacturing a Fresnel lens angular lens segment comprising: a) feedingstep of feeding raw plastic sheet to a roller extruder having a blankroller and a die roller, the die roller having a first roller inner edgeand a first roller outer edge, having two peripheral lens dies, a firstlens die and a second lens die, which are proximally joined at a diejunction proximal to the first roller inner edge and have a primaryangular displacement of approximately one hundred eighty degreesproximal to the first roller outer edge, and having peripheral Fresnelfacet dies; and b) extruding step of extruding, for a revolution of thedie roller, the angular lens segment, the angular lens segmentcomprising a first lens subsegment and a second lens subsegment, thefirst lens subsegment and the second lens subsegment respectively beingimpressed between the first lens die and the second lens die, the firstlens subsegment having its minimum circumferential dimension proximal tothe die junction and it maximum circumferential dimension proximal tothe first roller outer edge where the primary angular displacement isapproximately one hundred eighty degrees, and the second lens subsegmenthaving its minimum circumferential dimension proximal to the firstroller outer edge where the first lens die and the second lens die havea reverse angular displacement of approximately one hundred eightydegrees and its maximum circumferential dimension proximal to the firstroller inner edge wherein the first lens die and the second lens diehave a maximum reverse angular displacement, and the Fresnel facet diesimpressing Fresnel facet groves on the first lens subsegment and thesecond lens subsegment so as to provide a desired facet groove patternin the angular lens segment.
 22. Method for manufacturing a Fresnel lensangular lens segment comprising: a) feeding step of feeding raw plasticsheet to a roller extruder having a blank roller and a die roller, thedie roller having a first roller inner edge and a first roller outeredge, having two peripheral lens dies, a first lens die having a firstdie end and a second lens die having a second die end, and havingperipheral Fresnel facet dies, the first lens die and the second lensdie being proximally joined at a die junction which is proximal to thefirst roller inner edge, and the first lens die and the second lens diebeing angularly separated by a primary angular displacement whichincreases approximately linearly with longitudinal distance from the diejunction to the first die end and the second die end, the first die endand the second die end being proximal to the first roller outer edge,and the primary angular displacement between the first die end and thesecond die end being approximately one hundred eighty degrees; and b)extruding step of extruding, for a revolution of the die roller, theangular lens segment, the angular lens segment comprising a first lenssubsegment and a second lens subsegment, the first lens subsegment andthe second lens subsegment respectively being impressed between thefirst lens die and the second lens die, the first lens subsegment havingits minimum circumferential dimension proximal to the die junction andit maximum circumferential dimension proximal to the first roller outeredge where the primary angular displacement is approximately one hundredeighty degrees, and the second lens subsegment having its minimumcircumferential dimension proximal to the first roller outer edge wherethe first lens die and the second lens die have a reverse angulardisplacement of approximately one hundred eighty degrees and its maximumcircumferential dimension proximal to the first roller inner edgewherein the first lens die and the second lens die have a maximumreverse angular displacement, and the Fresnel facet dies impressingFresnel facet groves on the first lens subsegment and the second lenssubsegment so as to provide a desired facet groove pattern in theangular lens segment.
 23. Method for manufacturing a Fresnel lensangular lens segment comprising: a) feeding step of feeding raw plasticsheet to a roller extruder having a first die roller and a second dieroller, the first die roller having a first roller inner edge and afirst roller outer edge, having two peripheral lens dies, a first lensdie and a second lens die, which are proximally joined at a die junctionproximal to the first roller inner edge and have a primary angulardisplacement of approximately one hundred eighty degrees proximal to thefirst roller outer edge, and having peripheral first Fresnel facet dies,and the second die roller having peripheral second Fresnel facet dies;and b) extruding step of extruding, for a revolution of the first dieroller and the second die roller, the angular lens segment, the angularlens segment comprising a first lens subsegment and a second lenssubsegment, the first lens subsegment and the second lens subsegmentrespectively being impressed between the first lens die and the secondlens die, the first lens subsegment having its minimum circumferentialdimension proximal to the die junction and it maximum circumferentialdimension proximal to the first roller outer edge where the primaryangular displacement is approximately one hundred eighty degrees, andthe second lens subsegment having its minimum circumferential dimensionproximal to the first roller outer edge where the first lens die and thesecond lens die have a reverse angular displacement of approximately onehundred eighty degrees and its maximum circumferential dimensionproximal to the first roller inner edge wherein the first lens die andthe second lens die have a maximum reverse angular displacement, and thefirst Fresnel facet dies impressing first Fresnel facet groves on theouter segment surface of the first lens subsegment and the second lenssubsegment so as to provide a desired first facet groove pattern in theouter segment surface of the angular lens segment, and the secondFresnel facet dies impressing second Fresnel facet grooves on an innersegment surface of the first lens subsegment and the second lenssubsegment so as to provide a desired second facet groove pattern in theinner segment surface.
 24. Method for manufacturing a Fresnel lensangular lens segment comprising: a) feeding step of feeding raw plasticsheet to a roller extruder having a first die roller and a second dieroller, the first die roller having a first roller inner edge and afirst roller outer edge, having two peripheral lens dies, a first lensdie having a first die end and a second lens die having a second dieend, and having peripheral first Fresnel facet dies, the first lens dieand the second lens die being proximally joined at a die junction whichis proximal to the first roller inner edge, and the first lens die andthe second lens die being angularly separated by a primary angulardisplacement which increases approximately linearly with longitudinaldistance from the die junction to the first die end and the second dieend, the first die end and the second die end being proximal to thefirst roller outer edge, and the primary angular displacement betweenthe first die end and the second die end being approximately one hundredeighty degrees, and having peripheral first Fresnel facet dies, and thesecond die roller having peripheral second Fresnel facet dies; and b)extruding step of extruding, for a revolution of the die roller, theangular lens segment, the angular lens segment comprising a first lenssubsegment and a second lens subsegment, the first lens subsegment andthe second lens subsegment respectively being impressed between thefirst lens die and the second lens die, the first lens subsegment havingits minimum circumferential dimension proximal to the die junction andit maximum circumferential dimension proximal to the first roller outeredge where the primary angular displacement is approximately one hundredeighty degrees, and the second lens subsegment having its minimumcircumferential dimension proximal to the first roller outer edge wherethe first lens die and the second lens die have a reverse angulardisplacement of approximately one hundred eighty degrees and its maximumcircumferential dimension proximal to the first roller inner edgewherein the first lens die and the second lens die have a maximumreverse angular displacement, and the first Fresnel facet diesimpressing first Fresnel facet groves on an outer surface of the firstlens subsegment and the second lens subsegment so as to provide adesired first facet groove pattern in the angular lens segment, and thesecond Fresnel facet dies impressing second Fresnel facet grooves on aninner surface of the first lens subsegment and the second lenssubsegment so as to provide a desired second facet groove pattern on theinner surface of the angular lens segment.
 25. Method for manufacturingFresnel lens angular segments comprising: a) feeding step of feeding rawplastic sheet to a roller extruder having a blank roller and a dieroller, the die roller having two peripheral lens dies and peripheralFresnel facet dies; b) extruding step of forming and extruding, for eachsuccessive revolution of the die roller, an extruded lens wafer from theraw plastic sheet, and impressing in the lens wafer by the lens dies foreach revolution of the die rollers, an angular lens segment from thelens wafer, the angular lens segment comprising an inner angular lenssubsegment and an outer angular lens subsegment, the lens diesimpressing the inner lens subsegment and the outer lens subsegment asthe die roller makes the complete revolution, the inner lens subsegmentand the outer lens subsegment being impressed in an inverted positionwith respect to each other in the lens wafer, the Fresnel facet diesimpressing Fresnel facet grooves in the inner lens subsegment and theouter lens subsegment so as to provide a desired facet groove pattern inthe angular lens segment.
 26. Method for manufacturing Fresnel lensangular segments comprising: a) feeding step of feeding raw plasticsheet to a roller extruder having a first die roller and a second dieroller, the first die roller having two peripheral lens dies andperipheral first Fresnel facet dies, and the second die roller havingperipheral second Fresnel facet dies; b) extruding step of forming andextruding, for each successive revolution of the die rollers, anextruded lens wafer from the raw plastic sheet, and impressing in thelens wafer by the lens dies for each revolution of the die rollers, anangular lens segment from the lens wafer, the angular lens segmentcomprising an inner angular lens subsegment and an outer angular lenssubsegment, the lens dies impressing the inner lens subsegment and theouter lens subsegment as the die roller makes the complete revolution,the inner lens subsegment and the outer lens subsegment being impressedin an inverted position with respect to each other in the lens wafer,the first Fresnel facet dies and the second Fresnel facet diesimpressing Fresnel facet grooves on opposing surfaces of the inner lenssubsegment and the outer lens subsegment so as to provide a desiredfacet groove pattern in the angular lens segment.
 27. Method formanufacturing a Fresnel lens angular lens segment comprising: a) feedingstep of feeding raw plastic sheet to a roller extruder having a blankroller and a die roller, the die roller having a pair of generallylongitudinal peripheral lens dies, and peripheral Fresnel facet dies;and b) extruding step of extruding, for a revolution of the die roller,the angular lens segment, the angular lens segment comprising a firstlens subsegment and a second lens subsegment, the first lens subsegmenthaving a first inner edge with a first inner generally circumferentialdimension, a first outer edge with a first outer generallycircumferential dimension, a first left edge with a first left dimensionand a first right edge with a first right dimension, the second lenssubsegment having a second inner edge with a second inner generallycircumferential dimension, a second outer edge with a second outergenerally circumferential dimension, a second left edge with a secondleft dimension, and a second right edge with a second right dimension,the first outer generally circumferential dimension being roughly equalto the second inner generally circumferential dimension providing forthe second lens subsegment to fit against the first lens subsegment withthe second inner edge fitting against the first outer edge for assemblyof an angular lens segment, the generally longitudinal peripheral lensdies impressing the first left edge, the first right edge, the secondleft edge and the second right edge, the end lens dies impressing thefirst inner edge, the first outer edge, the second inner edge and thesecond outer edge, and the Fresnel facet dies impressing Fresnel facetgroves on the first lens subsegment and the second lens subsegment so asto provide a desired facet groove pattern in the angular lens segment.28. Method for manufacturing a Fresnel lens angular segment comprising:a) feeding step of feeding raw plastic sheet to a roller extruder havinga blank roller and a die roller, the die roller having a generallycircumferential lens die, a longitudinal peripheral lens die, andperipheral Fresnel facet dies; and b) extruding step of extruding, for arevolution of the die roller, the angular lens segment, the angular lenssegment comprising a first lens subsegment and a second lens subsegment,the first lens subsegment having a first inner edge with a first innergenerally circumferential dimension, a first outer edge with a firstouter generally circumferential dimension, a first left edge with afirst left dimension and a first right edge with a first rightdimension, the second lens subsegment having a second inner edge with asecond inner generally circumferential dimension, a second outer edgewith a second outer generally circumferential dimension, a second leftedge with a second left dimension, and a second right edge with a secondright dimension, the first outer generally circumferential dimensionbeing roughly equal to the second inner generally circumferentialdimension providing for the second lens subsegment to fit against thefirst lens subsegment with the second inner edge fitting against thefirst outer edge for assembly of an angular lens segment, the generallycircumferential peripheral lens dies impressing the first left edge andthe second left edge, the longitudinal lens die impressing the firstinner edge, the first outer edge, the second inner edge and the secondouter edge, and the Fresnel facet dies impressing Fresnel facet grooveson the first lens subsegment and the second lens subsegment so as toprovide a desired facet groove pattern in the angular lens segment. 29.Method for manufacturing a Fresnel lens angular lens segment comprising:a) feeding step of feeding raw plastic sheet to a roller extruder havinga first die roller and a second die roller, the first die roller havinga pair of generally longitudinal peripheral lens dies, and peripheralfirst Fresnel facet dies, and the second die roller having peripheralsecond Fresnel facet dies; and b) extruding step of extruding, for arevolution of the die rollers, the angular lens segment, the angularlens segment comprising a first lens subsegment and a second lenssubsegment, the first lens subsegment having a first inner edge with afirst inner generally circumferential dimension, a first outer edge witha first outer generally circumferential dimension, a first left edgewith a first left dimension and a first right edge with a first rightdimension, the second lens subsegment having a second inner edge with asecond inner generally circumferential dimension, a second outer edgewith a second outer generally circumferential dimension, a second leftedge with a second left dimension, and a second right edge with a secondright dimension, the first outer generally circumferential dimensionbeing roughly equal to the second inner generally circumferentialdimension providing for the second lens subsegment to fit against thefirst lens subsegment with the second inner edge fitting against thefirst outer edge for assembly of an angular lens segment, the generallylongitudinal peripheral lens dies impressing the first left edge, thefirst right edge, the second left edge and the second right edge, theend lens dies impressing the first inner edge, the first outer edge, thesecond inner edge and the second outer edge, and the first Fresnel facetdies impressing first Fresnel facet grooves on a front surface of thefirst lens subsegment and the second lens subsegment and the secondFresnel facet dies impressing second Fresnel facet grooves on a rearsurface of the first lens subsegment and the second lens subsegment, soas to provide a desired facet groove pattern in the angular lenssegment.
 30. Method for manufacturing a Fresnel lens angular segmentcomprising: a) feeding step of feeding raw plastic sheet to a rollerextruder having a first die roller and a second die roller, the firstdie roller having a generally circumferential lens die, a longitudinalperipheral lens die, and peripheral first Fresnel facet dies, and thesecond die roller having peripheral second Fresnel facet dies; and b)extruding step of extruding, for a revolution of the die roller, theangular lens segment, the angular lens segment comprising a first lenssubsegment and a second lens subsegment, the first lens subsegmenthaving a first inner edge with a first inner generally circumferentialdimension, a first outer edge with a first outer generallycircumferential dimension, a first left edge with a first left dimensionand a first right edge with a first right dimension, the second lenssubsegment having a second inner edge with a second inner generallycircumferential dimension, a second outer edge with a second outergenerally circumferential dimension, a second left edge with a secondleft dimension, and a second right edge with a second right dimension,the first outer generally circumferential dimension being roughly equalto the second inner generally circumferential dimension providing forthe second lens subsegment to fit against the first lens subsegment withthe second inner edge fitting against the first outer edge for assemblyof an angular lens segment, the generally circumferential peripherallens dies impressing the first left edge and the second left edge, thelongitudinal lens die impressing the first inner edge, the first outeredge, the second inner edge and the second outer edge, and the firstFresnel facet dies impressing first Fresnel facet grooves on a frontsurface of the first lens subsegment and the second lens subsegment andthe second Fresnel facet dies impressing second Fresnel facet grooves ona rear surface of the first lens subsegment and the second lenssubsegment, so as to provide a desired facet groove pattern in theangular lens segment.